Problem: In geometry class, the girl to boy ratio is $3$ to $2$. If there are a total of $10$ students, how many girls are there?
Solution: A ratio of $3$ girls to $2$ boys means that a set of $5$ students will have $3$ girls and $2$ boys. A class of $10$ students has $2$ sets of $5$ students. Because we know that there are $3$ girls in each set of $5$ students, the class must have $2$ groups of $3$ girls each. There is a total of $6$ girls in geometry class.